Plastic insulated wire for communications use, for example, generally is made by extruding plastic insulation about a moving wire. For identification purposes during use of the insulated wire, the insulation extrudate generally includes a colorant. In order to change colors, the extruding equipment has to be purged prior to its use with a plastic material having a different colorant. Obviously, this requires much time and wastes much material. Furthermore, colorant materials used for such purpose generally are metallic based materials which results in an increased number of faults in the final product.
It would be far simpler if all the manufactured wire could be made with a neutral insulation material such as a clear plastic, for example, and then colored subsequently. The changeover of colors in a marking apparatus, positioned after an extruder along a manufacturing line, is far less costly than changeover in the extruder and results in improved quality and performance.
The application of a colorant material to a moving wire may be accomplished in any of several ways. For example, it could be applied by a contact device such as a wheel or it could be applied in a spray or stream by a nozzle.
In the art of applying bands of different colors onto insulated wire, it is known to employ apparatus including a pair of hollow discs mounted on opposite sides of a wire advancing longitudinally along a predetermined path. Each of the discs is provided with a peripheral row of spaced radially directed apertures and colored fluid or ink, which is supplied to the discs, is forced outwardly through the apertures in the form of streams as the discs rotate. Streams of ink from one disc of the pair engage the advancing wire and apply color markings onto one side thereof at regular intervals. The other disc of the pair, which is longitudinally offset from the one disc, applies markings of the same color to the opposite side of the wire in registration with the markings applied by the one disc to form annular bands of the color on the wire at regularly spaced intervals. See H. L. Woellner U.S. Pat. No. 3,176,650. Such an arrangement has been found to be unsuitable for applying colorant to substantially all the surface of a plastic insulated wire.
In the application of colorant material to plastic insulated wire, difficulty has been encountered in controlling the shape and opacity of colored markings on the plastic insulated wire. Difficulty has been experienced where it is desirable or necessary to advance the insulated wire at a high rate of speed. As liquid colorant material is sprayed onto the insulated wire, generally at an angle of 90.degree. to the path of travel of the insulated wire, the liquid colorant material could be accelerated instantaneously up to wire speed, thereby causing high impact at high wire speeds. The liquid may rebound off the wire, causing poor opacity.
Preferably, the sought after arrangement for applying a colorant material to substantially the entire peripheral surface of a plastic insulated wire is non-contacting. One reason for this relates to the kinds of plastic materials which comprise the extrudate that is applied to the wire. In today's world, fluoropolymers have been found to possess a number of desirable attributes. Accordingly, their use has proliferated. However, unlike some polyolefins such as polyvinyl chloride (PVC), for example, which are somewhat porous thereby allowing any colorant material to be applied to it either before or after it has been cooled, fluoropolymers generally are non-porous, necessitating application of colorant material thereto while in a hot state after extrusion but prior to cooling. Should a contact device be used immediately after the extrudate has been applied, it would result in widespread deformation of the plastic material.
Further of importance is the need to stabilize the moving wire against undulatory movement. Otherwise, the resulting coloring could be non-uniform. Also, undesired undulations could cause the moving colored wire to engage undesirably wire guides or other equipment.
Apparatus had been available in the marketplace for the surface coloring of insulated wires having a relatively large diameter-over-dielectric (DOD) and cables in line with an extruder, allowing the extrusion of plastic material in one basic color. Such a system involved a high pressure ink pump and three nozzles attached to a ring and spaced about the periphery of an elongated material which was advanced through the ring.
What is needed and what is not provided in the prior art are methods and apparatus for applying a colorant material to an elongated material having a relatively small cross section transverse to its longitudinal axis in a manner which allows the elongated material to be moved at a relatively high rate of speed. The sought after methods and apparatus should be capable of applying the colorant material in tandem with an extruder which applies plastic insulation material and the application of the colorant material to the surface of the insulation should be such that it covers substantially the entire surface thereof.